Outlook software in Microsoft 365 (Office 365) has an option to dismiss reminders on past appointments. Enable it in File > Options > Advanced > Automatically dismiss reminders for past calendar events.

The first macro is for those Outlook users who use Outlook's calendar as a journal and create appointments in the past. If you don't set the reminder to none, it will fire as soon as you create the appointment.

The second macro is for anyone who needs to remove reminders from old appointments.

We put appointments on the calendar that are in the past for record-keeping purposes. How can I stop the reminders for these appointments and keep reminders for future appointments?

To test, click in the Application_Startup macro and click the Run button.

Private WithEvents Items As Outlook.Items

Private Sub Application_Startup()
  Dim Ns As Outlook.NameSpace

  Set Ns = Application.GetNamespace("MAPI")
  Set Items = Ns.GetDefaultFolder(olFolderCalendar).Items
End Sub

Private Sub Items_ItemAdd(ByVal Item As Object)
  On Error Resume Next
  Dim Appt As Outlook.AppointmentItem

  If TypeOf Item Is Outlook.AppointmentItem And Item.Start < Now() Then
    Set Appt = Item

     Appt.ReminderSet = False
     Appt.Save
  End If

End Sub

Remove reminders on existing appointments

To remove reminders from existing appointments, use this VBA code. The reminders are removed from all appointments in the default calendar folder that have a start time prior to "now".

Public Sub RemoveReminder()

Dim Ns As Outlook.NameSpace
Dim Appt As Object
Set Ns = Application.GetNamespace("MAPI")
Set Items = Ns.GetDefaultFolder(olFolderCalendar).Items

For Each Appt In Items

On Error Resume Next

If Appt.Start < Now() Then
    Appt.ReminderSet = False
    Appt.Save
End If

Next

Set App = Nothing
Set Ns = Nothing

End Sub